The present application relates to the application of a workpiece treating medium to a screen.
More particularly, the invention relates to apparatus for applying a workpiece treating medium to a screen.
Still more specifically, the present invention relates to apparatus for applying workpiece treating medium to a space which is open to the screen, and means for controlling the pressure under which the medium is applied.
Basic apparatus for this purpose are already known from the screen-printing art, where so-called slit or box squeegees are placed superjacent to a printing screen and the liquid or pasty printing ink is admitted into the interior of the squeegee (compare German Patent No. 2,300,290).
It is also known that the treating medium may be printing ink that has been converted to foamed state (compare German Published Application OS 2,523,062).
The use of treating medium--the term is used herein not merely in relation to printing ink but relative to any foamable medium that can be applied to a workpiece, e.g. fireproofing liquid, mothproofing liquid, appearance-enhancing liquid, etc.--in foamed condition has the advantage of much more uniform application of the medium to the workpiece than would otherwise be the case. The reason is that each foam bubble contains only a small amount of the liquid which it yields when it bursts, so that uniform application is assured. On the other hand, a prerequisite of success with foamed treating medium is that a screen be interposed between it and the workpiece. The workpiece surface is never as uniform as the screen surface and it is this factor which assures uniform bursting of the foam bubbles at the foam/screen interface.